Recently, display devices have been used as information display for observers in various devices. Currently, instead of the cathode-ray tube which was the mainstream, new flat-panel display devices using liquid crystal, plasma, Electro-Luminescence (EL), Field Emission Display (FED), and the like have appeared. Particularly, a liquid crystal display device can be manufactured from a small-sized type to a large-sized type and is the representative flat-panel display device, in now.
Such a flat-panel display device is provided with a display area in which plural pixels are arranged in a matrix shape. In the display area, plural scanning lines and plural signals lines are formed and intersect each other to define pixels. In each pixel, a switching element having an electrode connected to the scanning line or the signal line and a pixel electrode connected to the switching element are formed. A voltage input from the signal line is applied to the pixel electrode via the switching element and is applied to an electro-optical medium such as a liquid crystal or an electroluminescence material to contribute to display. A thin-film transistor (TFT) is often used as the switching element.
When the TFT is formed, there may be a problem such as the pixels or the lines in the display area are damaged or dielectric breakdown of an insulating film is caused, due to static electricity during manufacturing. For the purpose of protecting the pixels in the display area from dielectric breakdown, dummy pixels are generally formed outside the display area (for example, see Japanese Unexamined Patent Application Publication No. Hei 03-045934).
A reversely-staggered type thin-film transistor which is subjected to back channel etching is generally used as a thin-film transistor for a liquid crystal display device. Further, an array structure, in which TFTs and pixel electrodes are separately formed with an insulating film interposed therebetween and the TFTs and the pixel electrodes are connected via contact holes formed in the insulating film, is often used. In making of such a structure, a method including forming an insulating film to cover formed TFTs, forming contact holes in the insulating film on the TFTs, forming pixel electrodes on the insulating film, and then connecting the TFTs and the pixel electrodes via contact holes is often used (for example, see Japanese Unexamined Patent Application Publication No. Hei 10-268353).
The main purpose of forming an insulating film on a TFT formed in a pixel is to protect the TFT from liquid crystal and to suppress an unnecessary electric field from being applied to the liquid crystal from the TFT. If there is a trouble in which a predetermined insulating film is not formed on a TFTs, a voltage is applied directly to the liquid crystal from the TFT. If such voltage application is continuously performed for a long time, the liquid crystal is charged or denatured, thereby finally causing display failure. However, since an application of a voltage for a long time is required until the display failure occurs and apparent display abnormality does not occur immediately after being turned on, there is a problem that it is difficult to find the trouble in inspection during manufacturing.
Further, when an insulating film is not formed, there is concern about a short circuit between the pixel electrode formed on the insulating film and the TFT, but the pixel electrode and the drain electrode of the TFT are originally connected to each other via a contact hole. Accordingly, if the pixel electrode overlaps only the drain electrode in a top view, the problems is not caused even when the insulating film therebetween is not formed.
On the other hand, when the pixel electrode is formed to overlap a signal line below the insulating film in a top view and the insulating film is not formed, the potential of the signal line is applied directly to the pixel electrode and thus abnormality can be immediately found as display failure. However, if the pixel electrode is formed in the above-mentioned way, capacitance is formed between the pixel electrode and the signal line, and thus there is a problem in that the supply of a signal voltage is delayed and does not follow an increase in the number of pixels accompanied with an increase in screen size.
Accordingly, the signal line is often formed so as not to overlap the pixel electrode. In this case, as described above, there remains a problem in that abnormality of display failure is not immediately found even when the insulating film is not formed. That is, since the application of a voltage for a long time is required up to display failure, there is a problem in that much time is required for inspection. Since the time required for the application of a voltage is greatly varied depending on array substrates, there is a possibility that the array substrates will shipped, as is.